Most UV LED curing systems emit light that diverges from the source — spreading outward as it travels away from the lamp. For many applications, this divergence is inconsequential. For others, it is the source of a process limitation that no amount of irradiance adjustment can overcome. Collimated UV light solves a specific problem: getting UV energy into confined spaces and through narrow apertures where diverging beams simply cannot reach.
What Collimation Means
Light is collimated when its rays travel parallel to each other rather than diverging from a point or converging toward a focal plane. A perfectly collimated beam maintains a constant diameter regardless of propagation distance, delivering the same irradiance per unit area at 5 mm and 500 mm from the source.
In practice, perfect collimation is not achievable. Real optical systems produce beams with small divergence angles — typically measured in milliradians or degrees — but the divergence is small enough that the beam diameter changes slowly with distance and the beam can travel through narrow openings with minimal loss.
The sun is a natural example of an approximately collimated light source: because it is extremely far away, its light rays are nearly parallel when they reach Earth. Artificial collimated light sources use lenses, mirrors, or parabolic reflectors to reshape a diverging source into a parallel beam.
Why Standard UV LED Output Diverges
A UV LED emits light from a small semiconductor junction area in a Lambertian pattern — intensity is proportional to the cosine of the angle from the normal to the emitting surface. This produces a hemispherical emission pattern with no preferred direction. Light guides accept a portion of this output within their numerical aperture and deliver it to the cure head, where it exits in a cone defined by the guide’s NA. The resulting beam at the cure head is diverging, not collimated.
The divergence angle for a typical light guide output ranges from roughly 15° to 30° half-angle, depending on the guide’s NA. This means that the spot diameter increases with working distance, and the irradiance decreases as the beam spreads.
Where Collimation Makes a Difference
For most UV curing applications — bonding exposed adhesive on a flat surface at a defined working distance — beam divergence is manageable. The cure head is positioned at a working distance where the spot size covers the bond area and irradiance is within specification.
Collimated UV output becomes important in several specific situations:
Curing through narrow channels or small apertures. Some assembly geometries require UV light to travel through a tube, a bore, a drilled hole, or a small gap in a housing to reach the adhesive. A diverging beam entering a narrow opening loses a substantial fraction of its energy to the walls before reaching the bond. A collimated beam with a diameter matched to the aperture passes through with minimal wall losses.
Maintaining irradiance over variable working distances. If the working distance to the cure surface varies from part to part — or if the cure head must operate at longer distances to clear obstructions — a collimated system maintains higher irradiance over that range than a diverging system, which spreads energy increasingly as distance grows.
Shadow curing in deep bondline recesses. Adhesive located at the bottom of a deep recess requires UV light to travel the full depth of the recess without illuminating the sidewalls. Collimated light maintains a consistent diameter through the recess depth, whereas diverging light scatters against the walls and may not reach the adhesive with adequate irradiance.
Uniform irradiance over a large flat area. Some collimated flood lamp systems produce highly uniform irradiance across large cure zones by combining collimation with array design, achieving uniformity specifications that would require a much longer working distance in a conventional diverging flood system.
How Collimation Is Achieved in UV LED Systems
Collimating lenses placed at the cure head exit reshape the diverging light guide output into a more parallel beam. A single collimating lens matched to the guide’s NA and beam diameter produces collimated or near-collimated output from a spot lamp system.
Parabolic reflectors collect light from a point or small-area source placed at the focal point and redirect it into a parallel beam. Reflector-based collimation is more commonly used in large-area flood systems than in spot lamp cure heads.
Compound lens arrays — combinations of microlenses and field lenses — can collimate the output of a large LED array uniformly across the aperture, producing collimated flood illumination over areas too large for a single lens to handle.
TIR (total internal reflection) optics mold the light from individual LEDs into highly controlled beam shapes before the output leaves the lamp module. These optics are often used in high-efficiency LED module designs where tight beam control is required from a dense array.
If you are designing a UV curing system for a confined space or long working distance application and need to evaluate collimated light options, Email Us and an Incure specialist will review your requirements.
Trade-Offs in Collimated UV Systems
Collimation adds optical complexity. Every lens surface introduces reflection losses — typically 3–5% per surface for uncoated optics — which reduce the total UV power reaching the cure surface. Anti-reflection coatings tuned to the LED’s wavelength recover much of this loss, but they add cost.
More importantly, collimating optics must be matched to the specific light guide or LED module in the system. A collimating lens designed for a guide with one NA will not produce well-collimated output from a guide with a different NA. This integration specificity means that UV spot lamp cure heads with collimating optics are not typically interchangeable between different lamp platforms.
For applications where diverging beam geometry is adequate, a collimating system adds cost and complexity without benefit. Collimation is the right solution when the application geometry specifically requires it — not as a general upgrade.
Measuring the Divergence of a Curing System
Beam divergence can be characterized by measuring spot diameter at multiple working distances and fitting the data to a linear relationship. The slope of the spot diameter versus distance curve gives the full divergence angle. This measurement, performed with a UV-sensitive beam profiler or UV-sensitive film exposed at multiple distances, provides a quantitative basis for evaluating whether a given system’s divergence is acceptable for the intended application geometry.
Contact Our Team to discuss collimated UV curing system options and evaluate whether collimation is appropriate for your application.
Visit www.incurelab.com for more information.